Composite structures have been known in the art for many years. Although composite structures can be formed in many different manners, one advantageous technique for forming composite structures is a fiber placement or automated collation process. According to conventional automated collation techniques, one or more ribbons of composite material (also known as composite strands or tows) are laid down on a substrate. The substrate may be a tool or mandrel, but, more conventionally, is formed of one or more underlying layers of composite material that have been previously laid down and compacted.
Conventional fiber placement processes utilize a heat source to assist in compaction of the plies of composite material at a localized nip point. In particular, the ribbon or tow of composite material and the underlying substrate are heated at the nip point to increase the tack of the resin of the plies while being subjected to compressive forces to ensure adhesion to the substrate. To complete the part, additional strips of composite material can be applied in a side-by-side manner to each layer and can be subjected to localized heat and pressure during the consolidation process.
Unfortunately, defects can occur during the placement of the composite strips onto the underlying composite structure. Such defects can include tow gaps, overlaps, dropped tows, puckers, and twists. Additionally, foreign objects and debris (FOD), such as resin balls and fuzz balls, can accumulate on a surface of the composite structure. Resin balls are small pieces of neat resin that build up on the surfaces of the fiber placement head as the pre-impregnated tows pass through the guides and cutters. The resin balls become dislodged due to the motion and vibration of the fiber placement machine, and drop on to the surface of the ply. If not removed, subsequent courses will cover the resin ball and create a bump in the laminate whereat there may be no compaction of the tows. Fuzz balls are formed when fibers fray at the edges of the tows and then break off as the tows are passed through the cutter assembly. The broken fibers collect in small clumps that fall onto the laminate and, if not removed, are covered by the next course.
Composite laminates fabricated by fiber placement processes are typically subjected to a 100% ply-by-ply visual inspection for both defects and FOD. Typically, these inspections are performed manually during which time the fiber placement machine is stopped and the process of laying materials halted until the inspection and subsequent repairs, if any, are completed. In the meantime, the fabrication process has been disadvantageously slowed by the manual inspection process and machine downtime associated therewith.